JP5176021B6 - Gas diffusion substrate - Google Patents

Description

  The present invention relates to a gas diffusion substrate, and more particularly to a gas diffusion substrate used in a fuel cell such as a polymer electrolyte membrane fuel cell. The invention further relates to a method for producing a gas diffusion substrate.

  A fuel cell is an electrochemical cell that includes two electrodes separated by an electrolyte. A fuel such as hydrogen or methanol is supplied to the anode and an oxide such as oxygen or air is supplied to the cathode. An electrochemical reaction occurs at the electrode, and the chemical energy of the fuel and oxide is converted to electrical energy and heat. Fuel cells are clean and efficient power sources that can replace traditional power sources such as internal combustion engines in both stationary and power applications. In proton exchange membrane (PEM) fuel cells, the electrolyte is a solid polymer membrane that is electronically insulating but ionically conductive.

  The main component of a polymer electrolyte fuel cell is known as a membrane electrode assembly (MEA) and consists essentially of five layers. The middle layer is a polymer film. There is an electrocatalyst layer on either side of the membrane, typically containing a platinum-based electrocatalyst. The electrode catalyst is a catalyst that promotes the electrochemical reaction rate. Finally, there is a gas diffusion substrate adjacent to each electrode catalyst layer. The gas diffusion substrate must allow reactants to reach the electrode catalyst layer and conduct current generated by the electrochemical reaction. Therefore, the substrate must be porous and conductive.

  The MEA can be configured in several ways. An electrode catalyst layer may be applied to the gas diffusion substrate to form a gas diffusion electrode. Two gas diffusion electrodes can be placed on either side of the membrane and stacked together to form a 5-layer MEA. Alternatively, an electrode catalyst layer may be provided on both sides of the film to form a catalyst coating film. Thereafter, a gas diffusion substrate is applied to both sides of the catalyst coating film. Finally, an MEA can be formed from a membrane coated with an electrode catalyst layer on one side, a gas diffusion substrate in contact with the electrode catalyst layer, and a gas diffusion electrode on the other side of the membrane. .

  Typical gas diffusion substrates include carbon paper (eg, Toray “trade name” paper available from Toray Industries, Japan), carbon woven fabric (eg, Zoltek “product” available from Zoltek Corporation, USA). Name ") or non-woven carbon fiber webs (e.g. Optimat 203 available from Technical Fiber Products (UK)). Carbon substrates are typically modified with particulate material embedded in the substrate or coated on a flat surface, or a combination of both. The particulate material is typically a mixture of carbon black and a polymer such as polytetrafluoroethylene (PTFE).

  US Pat. No. 6,511,768 discloses a gas diffusion substrate comprising a graphitized fiber web structure. The web is manufactured by employing a web structure formed from polyacrylonitrile (PAN) fibers and oxidizing and graphitizing the web. The graphitization step is performed at a temperature of 1500 to 2500 ° C. This type of high temperature processing requires significant energy input, which increases the cost of the manufacturing process.

  EP 791974 discloses a continuous production process for preparing a gas diffusion substrate without using a high temperature graphitization step. Carbon black is mixed with PTFE, and carbon fiber is coated with PTFE. The carbon black / PTFE mixture and the coated carbon fiber are mixed to form a slurry that is deposited on the movable mesh bed. The deposited layer is dried to form a gas diffusion substrate.

  We have attempted to provide a gas diffusion substrate material with improved conductivity compared to the substrate disclosed in EP 791974 and a method that does not require high temperature graphitization of the fibrous web Have attempted to achieve the material. The substrate must have conductivity, air permeability and water treatment properties suitable for use in fuel cells. The substrate should be strong and flexible enough to withstand further processing to the electrode and / or membrane electrode assembly.

Therefore, the present invention
Carbon fiber non-woven network, and the carbon fiber is graphitized, the non-woven network is not graphitized,
Comprising a mixture of graphite particles and a hydrophobic polymer disposed within the nonwoven network;
A gas diffusion substrate is provided wherein the longest dimension of at least 90% of the graphite particles is less than 100 μm.

  Graphitization is a process in which carbon is heated to at least 1500 ° C. and the crystal structure of carbon changes to a “graphite-like” form that is more similar to the structure of pure graphite. The carbon fiber is graphitized, but the nonwoven network is not graphitized and the carbon fiber nonwoven network is physically different from the graphitized network. The graphitized network appears to have higher conductivity and higher stiffness compared to the non-graphitized network made of graphitized carbon fibers.

  US Pat. No. 6,511,768 states that high fiber stiffness prevents the formation of web structures from graphitized fibers, but we have described the gas diffusion groups of the present invention. It has been found advantageous to use graphitized fibers to form a nonwoven network of fibers in the material. Since it is easier and more economical to treat individual fibers, it is preferred to use individual graphitized fibers rather than graphitizing the fiber network. Also, graphitization of the fiber network can result in undesirable non-flat structures due to anisotropic dimensional changes that occur during the graphitization process.

  US Pat. No. 6,511,768 states that graphitized web structures should be used to form gas diffusion substrates because they have high through-plane conductivity. Disclosure. The present inventors have found that a gas diffusion substrate having high conductivity can be achieved without using a graphitized web structure. In the present invention, high conductivity is achieved by placing fine graphite particles within a nonwoven network of graphitized carbon fibers. Fine graphite particles (the longest dimension of at least 90% of the graphite particles is less than 100 μm) provides the fibers with an alternative parallel conduction path, helping to connect adjacent fibers and thus improving the conductivity between the fibers Let

Graphitized carbon fibers are preferably carbon fibers formed by oxidizing and graphitizing polyacrylonitrile (PAN) fibers. Suitably, the average diameter of the carbon fibers is 0.1-20 μm, preferably 1-10 μm. The average length of the carbon fibers is suitably 1 to 20 mm, preferably 3 to 12 mm. The basis weight of the nonwoven fabric network (areal weight) is preferably a 10 to 50 g / ^{m 2,} preferably from 20 to 40 g / ^{m 2} (which is the weight of only carbon fibers, graphite particles or hydrophobic Does not include the weight of the conductive polymer). If the fiber network has a lower basis weight, the conductivity of the substrate may be reduced.

  In the nonwoven network, the carbon fibers are preferably oriented randomly in the x and y directions (in-plane) to form a two-dimensional isotropic structure. However, orientation in the x and y directions can be introduced depending on the method used to form the fiber network. When the fiber network is formed using conventional papermaking or wet laid nonwoven technology, there appears to be random orientation in the z direction (plane penetration).

  The graphite particles used in the present invention may be graphitized carbon black, but are preferably flaky graphite or spherical graphite. The longest dimension of at least 90% of the graphite particles is less than 100 μm, suitably 20 to 0.1 μm, preferably 5 to 0.1 μm. Fine graphite particles and very fine graphite particles are preferred. Larger particles can be difficult to keep in the fiber network. Preferably, the graphite particles are supplied as a colloidal suspension of graphite particles, the graphite particles being small enough to be retained within the colloidal suspension. Because small particles do not aggregate, a colloidal suspension of graphite particles is advantageous.

  The hydrophobic polymer is suitably a fluoropolymer such as polytetrafluoroethylene (PTFE) or fluorinated ethylene-propylene (FEP), preferably PTFE. The weight ratio of graphite particles to hydrophobic polymer is suitably 50: 1 to 2: 1, preferably 10: 1 to 4: 1. The weight ratio of graphite particles to carbon fibers is suitably 1: 2 to 10: 1, preferably 3: 5 to 5: 1. The relative amounts of graphite particles, hydrophobic polymer and carbon fiber are extremely important in determining the properties of the substrate. Increasing the proportion of the hydrophobic polymer increases the hydrophobicity of the substrate and increases the strength, but increasing the proportion of carbon fibers and graphite particles increases the conductivity. Because graphite particles have very low resistance, the relative amount of graphite particles has the greatest effect on conductivity.

  According to one aspect of the invention, there is a concentration gradient of graphite particles and hydrophobic polymer throughout the thickness of the fiber network. The expression “concentration gradient” means that the concentration changes gradually (but not necessarily linearly) from the first side to the second side of the network. Suitably, the amount of graphite particles and hydrophobic polymer on the first side is at least twice, preferably at least four times the amount of graphite particles and hydrophobic polymer on the second side.

  In another aspect of the invention, the graphite particles and the hydrophobic polymer are homogeneously disposed within the fiber network. That is, there is no concentration gradient across the thickness of the fiber network.

  In addition to the graphite particles and the hydrophobic polymer, the gas diffusion substrate may further include a binder formed by rapid low temperature carbonization of the phenolic resin. This binder fixes the nodes of the web structure and more closely bonds the graphite particles, thus increasing the strength of the substrate in the xy plane. Furthermore, the binder also reduces the compressibility of the material. The amount of carbonized phenolic resin binder is preferably 2 to 50% by weight based on the weight of the substrate. In contrast to graphitization performed at temperatures higher than about 1500 ° C., carbonization can be achieved at temperatures of about 800 ° C. Lower temperatures can be used, but the accompanying increase in conductivity is also reduced.

  According to a preferred embodiment of the present invention, the gas diffusion substrate is suitable for use in a fuel cell and thus has an “ex-situ” thickness of less than 400 μm, preferably a thickness of 100 to 250 μm. The thickness of the substrate can vary substantially with compression, such as occurs when assembled in a fuel cell stack.

  Preferably, when the substrate is used in a fuel cell, a base layer of carbon black and a hydrophobic polymer is present on at least one side of the substrate. The granular carbon black material is, for example, an oil furnace black such as Vulcan “trade name” XC72R (manufactured by Cabot Chemicals (USA)), or Shawinigan (manufactured by Chevron Chemicals (USA)) or Denka FX-35 (manufactured by Denka (Japan)). Acetylene black. The hydrophobic polymer is preferably polytetrafluoroethylene (PTFE). The base layer provides a continuous surface to which the catalyst layer is applied. If the gas diffusion substrate has a concentration gradient of graphite particles and hydrophobic polymer throughout the thickness of the substrate, the base layer is on the surface of the gas diffusion substrate where the concentration of graphite particles and hydrophobic polymer is higher Is preferred.

  The present invention further provides a gas diffusion electrode comprising the gas diffusion substrate according to the present invention and an electrode catalyst layer.

The electrocatalyst layer includes an electrocatalyst, and the electrocatalyst is a supported catalyst in which small metal particles are dispersed on a conductive granular carbon support even if it is a chopped metal powder (metal black) It may be. Preferably, the electrocatalytic metal is
(I) platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium),
(Ii) gold or silver,
(Iii) base metals,
Or an alloy or mixture containing one or more of these metals, or an oxide thereof. A preferred electrocatalytic metal is platinum, which may be alloyed with a noble metal such as ruthenium or a base metal such as molybdenum or tungsten. When the electrode catalyst is a supported catalyst, the supported amount of metal particles on the carbon support material is 10 to 90% by weight, preferably 15 to 75% by weight.

  The electrocatalyst layer preferably further comprises an ion conducting polymer, which is included to improve ionic conductivity within the layer.

  According to a preferred embodiment, the gas diffusion electrode is the cathode of the fuel cell and there is a concentration gradient of graphite particles and hydrophobic polymer throughout the thickness of the fiber network, the electrocatalyst layer comprising graphite particles and hydrophobic polymer It is in contact with the surface of the gas diffusion substrate having a higher concentration. Placing the most hydrophobic substrate surface adjacent to the catalyst layer prevents the catalyst layer from being clogged with water during fuel cell operation.

  The present invention further provides a membrane electrode assembly comprising a gas diffusion substrate according to the present invention. The membrane electrode assembly comprises a polymer electrolyte membrane interposed between two electrode catalyst layers. At least one of the gas diffusion substrates is a gas diffusion substrate according to the present invention and is adjacent to the electrode catalyst layer.

  The polymer electrolyte membrane may be any type of ion conducting membrane known to those skilled in the art. Preferably the membrane is proton conductive. In state-of-the-art membrane electrode assemblies, the membrane is based on perfluorinated sulfonic acid materials such as Nafion “trade name” (Dupont), Flemion “trade name” (Asahi Glass), and Aciplex “trade name” (Asahi Kasei). Often to do. The membrane may be a composite membrane and contains a proton conducting material and other materials that impart properties such as mechanical strength. For example, the membrane may comprise a proton conducting membrane and a matrix of silica fibers, as described in EP 875524. The membrane is suitably 200 μm thick, preferably less than 50 μm thick.

  According to a preferred embodiment, there is a concentration gradient of graphite particles and hydrophobic polymer throughout the thickness of the fiber network, and the electrocatalyst layer in the membrane electrode assembly is gas diffused with a higher concentration of graphite particles and hydrophobic polymer. It is in contact with the surface of the substrate.

The present invention is a method of forming a gas diffusion substrate according to the present invention, comprising:
a) depositing a graphitized carbon fiber slurry on the porous bed to form a wet fiber network;
b) preparing a suspension of graphite particles and a hydrophobic polymer;
The longest dimension of at least 90% of the graphite particles is less than 100 μm;
c) applying the suspension onto the wet fiber network;
further comprising: d) placing the suspension into the wet fiber network; and e) drying and firing the wet fiber network at a temperature not exceeding 1000 ° C. .

  This method does not require a separate step in which the dry fiber web is preformed, nor does it require a high temperature graphitization treatment, i.e. it does not need to be heated above 1500 ° C.

  The fiber slurry preferably comprises graphitized carbon fibers in a liquid such as water. The slurry can be prepared by mixing the fiber and water by mechanical or manual stirring. The slurry is deposited on a porous bed such as a papermaking wire or forming fabric. The slurry may be deposited using a number of techniques suitable for forming a wet laid nonwoven web, for example using a curtain coater or a wear coater, to provide a flat and thin slurry layer.

  The fiber slurry preferably contains a binder material such as polyvinyl alcohol (PVA), typically in the range of 5-15% of the total dry mass of the slurry. The fiber slurry preferably contains a viscosity modifier such as Texipol “trade name”, typically 0.5-1% of the total volume of the slurry. In one embodiment, the fiber slurry further contains a phenolic resin.

  When the slurry is deposited on the porous bed, a wet fiber network is formed. The wet fiber network is supported by the bed and collapses when removed from the bed.

  The longest dimension of at least 90% of the graphite particles is less than 100 μm, and preferably the longest dimension of at least 90% of the graphite particles is in the range of 0.1 to 5 μm. Fine graphite particles (0.1-100 μm) are preferred because they can be added to the fiber network through the filtration process. Larger particles do not penetrate the structure. Preferably, the graphite particles are supplied as a colloidal suspension of graphite particles, such as a colloidal solution of graphite particles.

  The suspension of graphite particles and hydrophobic polymer preferably comprises 1 to 10% solids in water. The suspension may be prepared by mixing a suspension of graphite particles, a suspension of a hydrophobic polymer and water by mechanical or manual stirring.

  The suspension is applied to the wet fiber network through a wear coater or curtain coater.

  The suspension is preferably placed in the wet fiber network using a suction device. In a preferred embodiment of the present invention, the suspension is applied to only one side of the wet fiber network and suction is applied to the other side of the wet fiber network. The suspension is sucked into the fiber network, but generally the suspension remaining near the substrate surface to which the suspension is applied rather than reaching the substrate surface to which the suction is applied. There are many. Thus, this method can be used to produce a gas diffusion substrate with a porosity gradient across the thickness of the substrate.

  The wet fiber network is dried and fired at a temperature not exceeding 1000 ° C, preferably not exceeding 400 ° C. This is preferred for many prior art methods where a high temperature graphitization step is required. Preferably, the firing temperature is sufficient to sinter the hydrophobic polymer and fix the binder in the fiber network, and is at least 270 ° C. When a phenolic binder is added to the fiber slurry, firing should be performed at 750-950 ° C if it is desired to completely carbonize the binder.

The present invention further provides an alternative method for preparing a gas diffusion substrate according to the present invention, which method comprises:
a) mixing graphite particles with a suspension of hydrophobic polymer to form a first slurry;
The longest dimension of at least 90% of the graphite particles is less than 100 μm;
b) mixing the graphitized carbon fiber, the liquid, and optionally a binder to form a second slurry;
c) mixing the first slurry and the second slurry to form a third slurry;
d) depositing the third slurry on the porous bed to form a fiber-containing layer; and e) drying and firing the fiber-containing layer at a temperature not exceeding 1000 ° C. is there.

  In this way, the graphite particles are completely contained within the carbon fiber web and provide a highly conductive gas diffusion substrate in a simple “one pot” process without the need for high temperature graphitization. Premixing the graphite particles with the hydrophobic polymer suspension ensures that the graphite particles are retained within the gas diffusion substrate.

  The suspension of hydrophobic polymer is preferably aqueous and may contain additional components such as surfactants. The solid content of the suspension is preferably 0.01% to 1% by weight. The graphite particles are mixed with the hydrophobic polymer suspension using a mixer such as a high shear mixer. The weight ratio of graphite particles to hydrophobic polymer is suitably 50: 1 to 2: 1, preferably 10: 1 to 4: 1. The inventors have found that the ratio of graphite particles to hydrophobic polymer affects the retention level of graphite particles in the gas diffusion substrate.

  A preferred binder for the second slurry is polyvinyl alcohol (PVA). The liquid is preferably water. The ratio of binder to fiber is preferably 1: 1 to 1:20, and the solid content of the second slurry is preferably less than 1% by weight. The fibers, optionally a binder, and a liquid are mixed using a mixer such as a high shear mixer. According to one embodiment, a phenolic resin may be added to the second slurry.

  The first slurry and the second slurry are preferably mixed together using a high shear mixer. It is impossible to mix graphite particles, hydrophobic polymer and graphitized carbon fiber in a single step, and it is necessary to pre-mix graphite particles and hydrophobic polymer. Otherwise, the graphite particles are not retained in the gas diffusion substrate.

  The third slurry is deposited on a porous bed which is preferably a papermaking wire or forming fabric. The third slurry may be deposited using a number of techniques, but is preferably deposited using a wear coater. When the third slurry is deposited on the bed, a fiber-containing layer is formed. The fibers form a network within the layer, and the graphite particles and the hydrophobic polymer are embedded within the fiber network. The concentration of graphite particles and hydrophobic polymer is substantially uniform throughout the thickness of the fiber-containing layer.

  The fiber-containing layer is dried and fired at a temperature not exceeding 400 ° C, preferably not exceeding 350 ° C. This is preferred for many prior art methods where a high temperature graphitization step is required. Preferably, the firing temperature is at least sufficient to sinter the hydrophobic polymer and fix the binder in the fiber network, at least 270 ° C. When phenolic resin is added to the second slurry, it must be fired at 750-950 ° C. to carbonize the binder.

  The method of the present invention may further include the step of applying a layer containing carbon black and a hydrophobic polymer to at least one surface of the fiber-containing layer.

  The present invention further provides a method of manufacturing a gas diffusion electrode, wherein a gas diffusion substrate is manufactured according to the method of the present invention and an electrode catalyst layer is deposited on the gas diffusion substrate. The electrocatalyst layer is placed using a coating method known to those skilled in the art, such as a printing method, a spray method or a doctor blade method.

  The invention will now be described with reference to examples, which are intended to illustrate but not limit the invention.

Example 1: By adding gas diffusion base fiber to water and stirring, 75% by weight of SGL C30 6 mm carbon fiber (graphitized PAN) (based on the weight of the solid component) and SGL C30 3 mm carbon A fiber slurry containing 25% by weight of fiber (graphitized PAN) was prepared. PVA binder (Solvron NL2003) (10% by slurry dry weight) and Texipol “trade name” 63-002 viscosity modifier (0.8% by slurry volume) were added. The fiber slurry was deposited on the papermaking wire using a wear coater to form a wet nonwoven fiber network.

  A graphite / PTFE slurry was prepared by mixing a graphite suspension (AquaDag 18%, Acheson) and PTFE suspension (Fluon GP1 solution, Asahi Glass) in a ratio of 4: 1. The slurry was applied to the wet fiber network using a curtain coater and placed in the fiber network using a suction device. The wet substrate was dried and fired at 385 ° C. for 15 minutes.

Example 2: A fiber slurry containing SGL C30 6 mm carbon fiber (graphitized PAN) was prepared by adding gas diffusion substrate fiber to water and stirring. PVA binder (Solvron NL2003) (15% by slurry dry weight) and Texipol “trade name” 63-002 viscosity modifier (0.6% by slurry volume) were added.

  A second slurry containing graphite particles and PTFE was prepared by mixing Timcal graphite flakes (T44) and PTFE suspension (Fluon GP1 solution, Asahi Glass) (6% by dry weight) in water.

  The two slurries were then mixed together in a forming tank and the fiber slurry was deposited on the papermaking wire using a wear coater to form a wet nonwoven fiber network interspersed with graphite particles.

  The wet substrate was dried and fired at 385 ° C. for 15 minutes.

Example 3 Membrane Electrode Assembly Example MEA1 was prepared using two gas diffusion substrates manufactured according to Example 1. A carbon / PTFE base layer was applied to one side of each gas diffusion substrate. With the base layer facing the membrane, a gas diffusion substrate was placed on either side of the catalyzed perfluorinated sulfonic acid membrane and the assembly was laminated together. Comparative Example MEA1 was prepared in exactly the same manner except that the gas diffusion substrate was Toray “trade name” TGP-H-060 paper having approximately the same thickness as the gas diffusion substrate according to Example 1.

  Both MEAs were tested at 65 ° C. in a fuel cell using a hydrogen pressure of 14.9 kPa and an air pressure of 14.9 kPa. FIG. 1 shows that the performance of Example MEA1 was comparable to that of Comparative Example MEA1.

FIG. 1 shows the performance of Example MEA1 and the relationship between the battery voltage and current density of Comparative Example MEA1.

Claims (21)

Carbon fiber non-woven network, and the carbon fiber is graphitized, the non-woven network is not graphitized,
Comprising a mixture of graphite particles and a hydrophobic polymer disposed within the nonwoven network;
A gas diffusion substrate, wherein the longest dimension of at least 90% of the graphite particles is less than 100 μm. The gas diffusion base material according to claim 1, wherein the basis weight of the nonwoven fabric network is 10 to 50 g / m ² .   The gas diffusion substrate according to claim 1 or 2, wherein the longest dimension of at least 90% of the graphite particles is 20 to 0.1 µm. The graphite particles becomes held in colloidal suspension, the gas diffusion substrate according to any one of claims 1-3.   The gas diffusion substrate according to any one of claims 1 to 4, wherein the weight ratio of the graphite particles to the hydrophobic polymer is 50: 1 to 2: 1.   The gas diffusion substrate according to any one of claims 1 to 5, wherein a weight ratio of the graphite particles to carbon fibers is 1: 2 to 10: 1.   The gas diffusion substrate according to any one of claims 1 to 6, wherein the gas diffusion substrate has a concentration gradient of the graphite particles and the hydrophobic polymer over the entire thickness of the nonwoven network.   The gas diffusion base material according to any one of claims 1 to 6, wherein the graphite particles and the hydrophobic polymer are uniformly arranged in the fiber network.   The gas diffusion base material according to any one of claims 1 to 8, comprising a carbonized phenol resin binder.   The gas diffusion substrate according to any one of claims 1 to 9, wherein a base layer of carbon black and a hydrophobic polymer is present on at least one surface of the gas diffusion substrate.   A gas diffusion electrode comprising the gas diffusion substrate according to any one of claims 1 to 10 and an electrode catalyst layer.   The gas diffusion electrode according to claim 11, wherein the electrode catalyst layer is in contact with the surface of the gas diffusion substrate having a higher concentration of graphite particles and hydrophobic polymer.   The membrane electrode assembly provided with the gas diffusion base material as described in any one of Claims 1-10.   A membrane electrode assembly comprising the gas diffusion electrode according to claim 11 or 12. A method for producing a gas diffusion substrate according to any one of claims 1 to 8,
a) depositing a graphitized carbon fiber slurry on the porous bed to form a wet fiber network;
b) preparing a suspension of graphite particles and a hydrophobic polymer;
The longest dimension of at least 90% of the graphite particles is less than 100 μm;
c) applying the suspension onto the wet fiber network;
d) A method of manufacturing comprising the steps of: placing the suspension into the wet fiber network; and e) drying and firing the wet fiber network at a temperature not exceeding 1000 ° C.   The manufacturing method according to claim 15, wherein in the step (d), the suspension is put into the wet fiber network using a suction device.   The manufacturing method according to claim 16, wherein the suspension is applied to one surface of the wet fiber network, and the suction is applied to the other surface of the wet fiber network. . A method for producing the gas diffusion substrate according to any one of claims 1 to 8,
a) mixing graphite particles with a suspension of hydrophobic polymer to form a first slurry;
The longest dimension of at least 90% of the graphite particles is less than 100 μm;
b) mixing the graphitized carbon fiber, the liquid, and optionally a binder to form a second slurry;
c) mixing the first slurry and the second slurry to form a third slurry;
d) depositing the third slurry on a porous bed to form a fiber-containing layer; and e) drying and firing the fiber-containing layer at a temperature not exceeding 1000 ° C. Method. The manufacturing method according to claim 18 , further comprising a step of applying a layer comprising carbon black and a hydrophobic polymer to at least one surface of the fiber-containing layer. The production method according to any one of claims 15 to 17, further comprising a step of imparting a layer comprising carbon black and a hydrophobic polymer to at least one surface of the fiber network . A gas diffusion substrate is manufactured by the manufacturing method according to any one of claims 15 to 20 , and an electrode catalyst layer is attached on the gas diffusion substrate. how to.

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